Nitrogen-substituted polyamides and process for obtaining same



I Patented Nov. 1947 NITROGEN SUBSTITUTED POLYAMIDES AND PROCESS FOROBTAINING SAME Theodore Le Sueur Cairns, Wilmington, DeL,

assignor to E. I. du Pont de Ncmours & Company, Wilmington, Del., acorporation of Delaware No Drawing.

Application June 8, 1944,

Serial No. 539,399

11 Claims. 1

This invention relates to synthetic polymeric materials and moreparticularly to chemically modified polyamides.

This application is a continuation-in-part of my application SerialNumber 445,635, filed June 3, 1942.

The above mentioned application is concerned with a new class ofpolyamides and their preparation by reacting a synthetic linearpolyamide having a hydrogen-bearing amid group in the presence of anoxygen-containing acid catalyst with formaldehyde and aformaldehyde-reactive organic compound having hydrogen attached to anelement of Group V and VI of Series 2 and 3 of the Periodic table. When'the formaldehydereactive organic compound used is an alcohol, theproducts are N-alkoxymethyl polyamides, i. e., products in which one ormore of the original hydrogen-bearing amide groups have been convertedinto groups of structure (If CH'zO R where R represents the organicradical of the alcohol, ROH, used. The present invention is concernedwith products formed in a similar manner using alcohols having acarboxyl group or a substituted carboxyl group such as a carboalkoxygroup.

This invention has as an object the preparation of new and usefulpolymeric materials. A further object is the conversion of syntheticlinear polyamides into water-soluble products or products which areeasily rendered water-soluble.

The objects are accomplished through the production of a new class ofnitrogen-substituted polyamides by a process comprising reacting apolyamide having hydrogen-bearing amide groups, in the presence of anoxygen-containing acid catalyst with formaldehyde and a substance of theclass consisting of hydroxy carboxylic acids and esters of hydroxycarboxylic acids. The above-mentioned acid catalysts areoxygen-containing acids having an ionization constant at least as greatas 9.6x and an equivalent conductance, measured at 25 C. in 0.01 Nconcentration, no greater than 370 ohmscm. This invention also embracesthe conversion of'the resultant products into salts and other carboxylicacid derivatives. 1

2 The invention is illustrated by the following examples in which partsare given by weight unless otherwise indicated.

Example 1 v The polyamide used in this example was an interpolyamideprepared by heating parts of hexamethylenediammonium adipate and '70parts of hexamethylenediammonium sebacamide under polymerizingconditions as described in U. S. Patent 2,252,554 until a high molecularweight fiberforming polymer was obtained.

Thirty parts Of the above interpolyamide was dissolved in 122 parts of100% formic acid at 70-80" C. and to this solution was added 20 parts ofparaformaldehyde suspended in 117 parts of methyl glycolate. After 10minutes reaction at 70 to 80 C., 28 parts of denatured ethanol was addedand the reaction mixture was poured into a solution of 100 parts ofsodium hydroxide dissolved in 1700 parts of water. This caused the N-carbomethoxymethoxymethyl substituted interdiffered from the originalinterpolyamide in that it contained substituted amide groups ofstructure 0 01120011100001 it-1L Emmplfe II A solution of parts ofpolyhexamethylene adipamide (intrinsic viscosity about 1.0) in a mixtureof 180 parts of formic acid and 60 parts of glycolic acid was preparedat 60 C. To

this solution was added a slurry of 60 parts paraformaldehyde, partsglycolic acid and 50 parts water. During the course of the next 35minutes at 60 C., 20 parts of water was added. The reaction mixture wasthen poured into approximately 1800 parts of a 1:1 (by volume) mixtureof water and acetone. A clear solution resulted from which the modifiedpolymer was precipitated by the addition of aqueous ammonia. Theprecipitated N-carboxymethoxymethyl polyhexamethylene adipamide wasfound to be readily soluble in aqueous ethanol, whereaspolyhexamethylene adipamide is insoluble in aqueous ethanol. Analysisshowed that the product contained 4.83% combined formaldehyde whichindicated that 15% of the amide groups in the original polyamide hadbeen converted into groups of formula omocmcoon i,

Example III A mixture of 100 parts fiber-forming polyhexamethyleneadipamide, 100 parts paraformaldehyde, 400 parts methyl glycolate, 15parts water and 3.4 parts 85% phosphoric acid was placed in a sealedvessel. The mixture was heated with agitation to 125 C. and maintainedbetween 125 and 135 C. for15 minutes. The mixture was then cooledrapidly to room temperature. The resulting clear viscous solution wasdiluted with 400 parts of an 80:20 (by volume) mixture Of ethanol andwater containing sumcient ammonia to neutralize the phosphoric acid, andthen the resulting solution was filtered. The clear filtrate was pouredinto about 7000 parts of water and the product, Ncarbomethoxymethoxymethylpolyhexamethylene adipamide, separated as asoft plastic mass which hardened during washing with water.

A solution of about 50 parts of the above-mentionedN-carbomethoxymethoxymethyl substituted polyamide," was prepared in 100parts methanol at 60 C. To this solution was added 7 parts potassiumhydroxide and the solution evaporated to dryness under reduced pressureto convert the N-carboxymethoxymethoxymethyl polyamide to thecorresponding potassium salt. The dry polymeric salt remaining afterevaporation of the methanol was found to dissolve readily in water.

Example IV A solution of 350 parts polyhexarnethylene adipamide in 1400parts of a mixture of 1.2 parts 90% formic acid and 0.8 part of aceticanhydride was prepared at 64 C. To this solution was added, over thecourse of 4 minutes, a suspension of 430 parts paraformaldehyde in 1330parts of methyl glycolate containing a trace of sodium hydroxide.Fifteen minutes after the beginning of the aldehyde addition 1330 partsof methyl glycolate was added and the mixture maintained at 60-64 C. fora further 15 minutes. The solution was then poured into a solution of2800 parts of acetone in 3500 parts of ice cold Water. Addition ofaqueous ammonia to this solution caused the modified polymer toprecipitate as a soft plastic mass. After washing with water and drying,the N-carbomethoxymethoxymethyl polyamide was found to have asaponification number of 141 which indicated that about 42% of the amidegroups in the original polyamide had been converted intoN-carbomethoxymethoxymethyl groups.

The above-mentioned N-carbomethoxymethoxymethyl polyhexamethyleneadipamide was readily converted into the corresponding sodium salt, 1.e., a polymeric salt containing groups of structure 0 CHsO CHzC 0 ON&

by heating a 20% solution of the ester in methanol at 60-65" 0. with thecalculated q ant y A solution of 15 parts of fiber-formingpolyhexamethylene adipamide in a mixture of 30 parts 90% formic acid and15 parts acetic anhydride was prepared at 60 C. To this was added asuspension of 15 parts paraformaldehyde in parts methyl lactate and 60parts formic acid. After maintaining the solution for 45 minutes at 60C., it was poured into a mixture of about 400 parts of acetone and 600parts of water. The modified polymer was precipitated by the addition ofsufficient ammonia to neutralize the acids present. The resultingfibrous white solid was found to have a saponiilcation number of 79which means that about 22% of the amide groups in the original polymershad been converted to groups of the formula This product can beconverted to a water soluble salt by the action of alkali by the methoddescribed in the foregoing example. I,

The polyamides used in the practice of this invention are of the generaltype described in U. S. Patents 2,071,250, 2,071,253 and 2,130,948.These polyamides, also referred to as nylons, generally speakingcomprise the reaction products of a linear polymer-forming compositioncontaining amide-forming groups, for example, reacting materialconsisting essentially of bifunctional molecules each containing tworeactive groups which are complementary to reactive groups in othermolecules and which include complementary amide-forming groups. Thesepolyamides can be obtained by the methods given in the above mentionedpatents and by other methods, for example, by self-polymerization of amonoaminomonocarboxylic acid, by reacting a diamine with a dibasiccarboxylic acid in substantially equimolecular amounts, or by reacting amonoaminomonohydric alcohol with a dibasic carboxylic acid insubstantially equimolecular amounts, it being understood that referenceherein to the amino acids, diamines, dibasic carboxylic acids, and aminoalcohols is intended to include the equivalent amide-forming derivainwhich X is oxygen or sulfur and R is hydrogen or a monovalenthydrocarbon radical, as an intean intrinsic viscosity, as defined in U.S. 2,130,948, 4

of at least 0.4.

Suitable acid catalysts are formic, acetic, chloroacetic,trimethylacetic, oxalic, p-toluenesulfonic, benzoic, maleic andphosphoric. When an hydroxyacid, rather than an ester thereof, is usedas a reactant, it is not necessary to add another acid as catalystalthough it is preferable to do so. The term "oxygen-containing acidcomprises mixtures of oxygen-containing acids and includes hydroxycarboxylic acids.

The mention of formaldehyde herein refers either to formaldehyde itselfor to other forms of formaldehyde, e. g., paraformaldehyde and trioxane,and also formaldehyde-liberating materials.

Examples of hydroxyacids which can be used are glycolic, lactic,tartaric, 10-hydroxydecanoic, 12-hydroxystearic, and their esters, e.g., the methyl, ethyl, butyl, methoxyethyl, cyclohexyl, and benzylesters. The corresponding nitriles (hydroxynitriles) can also be used.

The relative concentrations of reagents used can be varied considerably.Small amounts of formaldehyde (for example, 5% based on the weight ofthe polyamide) are operable and produce a definite change in theproperties of the polyamide used. It is desirable, however, to use atleast 25% formaldehyde, amounts varying from 25 to 200% of the polyamidebeing used to greatest advantage. The ratio of formaldehyde to hydroxyacid or ester can also be varied widely; generally, however, the molarratio of these two ingredients will be from 1:2 to 2:1, equimolar ratiosbeing preferred. When operating with an acid catalyst which is a solventfor the polyamide, e. g., formic acid, enough acid is generally used todissolve the polyamide. However, much smaller amounts 'are alsoefiective. When operating at elevated temperatures, 1 to 10% of acidbased on the weight of the polyamide is generally employed.

The reaction by which the new polyamides of this invention are preparedis advantageously carried out at temperatures ranging from 50 to 150 C.However, temperatures from about room temperature (25 C.) to thedecomposition temperature of the polyamide are operable.

The product of this invention are polyamides in which one or more of theamide groups in polymer chain has the structure R represents hydrogen,or a group capable of replacing acidic hydrogen, such as a monovalentthe hydrocarbon group, a metal, a basic organic radi cal, or theammonium radical. Examples of products in which R constitutes a, metalare the sodium and potassium salts described in the foregoing examples.Other salts are those in which one or more of the hydrogens in thecarboxyl groups, 1. e., R, are replaced by lithium, calcium,

compositions. The water soluble products can be.

used to make films. They can also be used as gelatin substitutes,thickeners for aqueous solutions,,and as modifying agents for viscoseand protein spinning solutions. For these and other uses the productscan be used alone or in conjunction with other materials, e. g.,pigments, dyes, plasticizers, resins, fillers, and the like.

As many widely different embodiments of this invention may be-madewithout departing from the spirit and scope thereof, it is to beunderstood 1 that this invention is not to be limited to specificembodiments thereof, except as defined in the appended claims.

I claim:

1. A nitrogen-substituted linear polyamide having a unit length of atleast 7 and containing in the polymer chain carbonamidegroups having thestructure 0 onioncoon' -CII\I wherein R represents a saturated aliphaticdivalent hydrocarbon radical containing from 1 to 17 carbon atoms, andR. represents a substituent selected from the group consisting ofhydrogen, metals, the ammonium radical, and monovalent hydrocarbonradicals containing from 1 to '7 carbon atoms.

2. The polyamide set forth in claim 1 in which R. is hydrogen.

3. The polyamide set forth in claim 1 in which R. is a m'onovalenthydrocarbon radical containing from 1 to 7 carbon atoms.

4. The polyamide set forth in claim 1 in which R. is a metal.

5. A nitrogen-substituted linear polyamide having a unit length of atleast '7 and containing in the polymer chain carbonamide groups havingthe structure 6. A nitrogen-substituted linear polyamide having a unitlength of at least 7 and containing in the polymer chain carbonamidegroups having the structure (I? $H2OCH1COOCH34 7. A process forobtaining a nitrogen-substituted polyamide which comprises reacting incontact with a catalyst a polyamide having a unit length of at least '7and having in the polymer chain hydrogen-bearing carbonamide groups withformaldehyde and a hydroxy carboxylic acid of the formula HORCOOH,wherein R is a saturated aliphatic divalent hydrocarbon radicalcontaining from 1 to 1'7 carbon atoms, said catalyst consisting of anoxygen containing acid having an ionization constant at least as greatas 9.6 10 and an equivalent conductance, measured at 25 C. in 0.01normal concentration, no greater than 3'70 ohmspm.

8. A process for obtaining a nitrogen-substituted polyamide whichcomprises reacting in contact with a catalyst a polyamide having a unitlength of at least 7 and having in the polymer chain hydrogen-bearingcarbonamide groups with formaldehyde and an ester of a hydroxycarboxylic acid, said ester having the formula HORCOOR', wherein R is asaturated aliphatic divalent hydrocarbon radical containing from 1 to 17carbon atoms and R is a monovalent hydrocarbon radical containing from 1to 7 carbon atoms, said catalyst consisting of an oxygen contaniing acidhaving an ionization constant at least as great as 9.6x 10" and anequivalent conductance, measured at 25 C. in 0.01 normal concentration,no greater'than 370 ohms- .0m.

9. A process for obtaining a nitrogen-substituted polyamide whichcomprises reacting in contact with a catalyst a polyamide having in thepolymer chain hydrogen-bearing carbonamide groups with formaldehyde andan ester of a hydroxy carboxylic acid, said ester having the formulaHORCOOR', wherein R is a saturated aliphatic divalent hydrocarbonradical containin from 1 to 1'7 carbon atoms and R is a monovalentREFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,276,309 Hummel et a1 Mar. 17,1942

